Iron crawlers, rubber crawlers and connecting link rubber crawlers have long been used as endless track travel devices for driving construction machines.
A conventional iron crawler is so constructed that steel track shoes are fitted to an endless connecting link pivotally connecting a pair of track links with pins (by welding or a bolt/nut mechanism). In this case, since mechanical connecting force between the track links is large, the iron crawler excels in durability. Besides, when a track shoe is abraded, it is exchangeable. However, the iron crawler has such trouble as a large creaky noise due to the track links, and driver's fatigue due to scanty cushion performance. Besides, if the iron crawler drives on pavements in urban areas, the road surface is damaged.
A conventional rubber crawler is so constructed that metal core bars and steel cords serving as a tensile reinforcing layer are embedded in a rubber elastic body. In this case, there is little noise, cushion performance is good, and the road surface is not damaged. Besides, since the rubber crawler is comparative lightweight, it can drive speedily. However, when the rubber crawler drives on sharp rocks or engineering wastes, cuts sometimes happen in the rubber part. When cuts get to any steel cords of the rubber crawler, the steel cords break due to cutting or corrosion. Therefore, the rubber crawler is unserviceable whether the rubber part is still available or not. Besides, when a tread lug rubber part is abraded by friction with the road surface, the whole rubber crawler must be integrally exchanged.
Recently, there has been a connecting link rubber crawler that makes good use of each merit of the conventional iron crawler and rubber crawler and makes up for each fault thereof. The conventional connecting link rubber crawler is so constructed that rubber pads (divided type or continuous type) are fitted to an endless connecting link pivotally connecting a pair of track links with pins (by welding or a bolt/nut mechanism). Here, a rubber pad is so made that a rubber elastic body is molded and fixed to a metal core. The connecting link rubber crawler has some merit as shown below. That is, since the mechanical connecting force between the track links is large, the connecting link rubber crawler excels in durability. When the tread lug rubber part of the rubber pad is abraded, only the rubber pad need be exchanged. Besides, the road surface is not damaged. However, since the connecting link rubber crawler uses connecting links composed of track links, the noise is large. Accordingly, since night engineering works are increased in urban areas recently, there is still an important noise problem in the connecting link rubber crawler.
Moreover, a detachable rubber crawler is disclosed in Japanese Patent Provisional Publication No. 133876 of 1992. The detachable rubber crawler is provided with tread lug rubber parts to be exchanged when they are abraded or lacking, or when their lug shape is changed in accordance with soil properties. The detachable rubber crawler, as shown in FIG. 19 and FIG. 20, comprises lug rubber parts 22 of one to two or more independent joint articles (which are detachable rubber pads) and a rubber belt part 26. The rubber belt part 26 is arranged on a crawler anti-tread (driving wheel) side with a tensile reinforcing layer 24 and core bars 25 embedded in a rubber elastic body 23. A lug rubber part 22 is provided with a steel metal core 27 and two or more steel pipes 29 each having a hole through which a bolt 28 for fastening the rubber belt part 26 welded to the metal core 27 is passed. A core bar 25 embedded in the rubber belt part 26 is provided with two or more holes with a fixed depth necessary for the steel pipes 29 and holes necessary for the bolts 28 on the same axis therewith. Here, in drawings, 30 is a nut, and 31 is a washer.
In the above-mentioned detachable rubber crawler, when the lug rubber parts are abraded or missing, they can be exchanged. Besides, since the detachable rubber crawler uses not connecting links but rather a rubber belt part, the noise problem can be quieted.
However, as for the rubber belt part, when a large driving force is added to the rubber crawler, a large shear force acts between the core bar and the steel cords, as in the conventional rubber crawler. When the large shear force acts repeatedly, the bonded portion between the core bar and the steel cords gradually causes a fatigue failure. Therefore, since the rubber belt part is damaged over time, the detachable rubber crawler can not completely make good use of the advantage of the exchangeable lug rubber part.